Playground HTML Data Types DOM JavaScript Input Output Debugging

Identifying and Correcting Errors

Become familiar with types of errors and strategies for fixing them

  • Review CollegeBoard videos and take notes on blog
  • Complete assigned MCQ questions if applicable

Code Segments

Practice fixing the following code segments!

Segment 1: Alphabet List

Intended behavior: create a list of characters from the string contained in the variable alphabet

Code:

%%js

var alphabet = "abcdefghijklmnopqrstuvwxyz";
var alphabetList = [];

for (var i = 0; i < 10; i++) {
	alphabetList.push(alphabet[i]);
}

console.log(alphabetList);

<IPython.core.display.Javascript object>

What I Changed

I changed…

I noticed that the for loop was pushing the integer i instead of the actual char. I simply added a line that pushes a char at incrementing indexes of the alphabet string instead of the integer itself.

Segment 2: Numbered Alphabet

Intended behavior: print the number of a given alphabet letter within the alphabet. For example:

"_" is letter number _ in the alphabet

Where the underscores (_) are replaced with the letter and the position of that letter within the alphabet (e.g. a=1, b=2, etc.)

Code:

%%js

// Copy your previous code to built alphabetList here
var alphabet = "abcdefghijklmnopqrstuvwxyz";
var alphabetList = [];

for (var i = 0; i < 10; i++) {
	alphabetList.push(alphabet[i]);
}

console.log(alphabetList);

let letterNumber = 5

for (var i = 0; i < alphabetList.length; i++) {
	if (i === letterNumber) {
        console.log('"' + alphabetList[i-1] + '" is letter number ' + letterNumber + ' in the alphabet');
	}
}

// Should output:
// "e" is letter number 5 in the alphabet

<IPython.core.display.Javascript object>

What I Changed

I changed…

I added the previous code logic to build to alphabet list. I then fixed the print statement to wrap the letter (i-1 because of 0 indexing) in quotations and fixed the string logic.

Segment 3: Odd Numbers

Intended behavior: print a list of all the odd numbers below 10

Code:

%%js

let odds = [];
let i = 1;

while (i <= 10) {
  odds.push(i);
  i += 2;
}

console.log(odds);

<IPython.core.display.Javascript object>

What I Changed

I changed…

I fixed the name of the list evens to odds and fixed the i value to print odd values instead of even values when incrementing by 2.

BELOW NOT EDITED

The intended outcome is printing a number between 1 and 100 once, if it is a multiple of 2 or 5

  • What values are outputted incorrectly. Why?
  • Make changes to get the intended outcome.
%%js

var numbers = []
var newNumbers = []
var i = 0

while (i < 100) {
    numbers.push(i)
    i += 1
}
for (var i of numbers) {
    if (numbers[i] % 5 === 0)
        newNumbers.push(numbers[i])
    else if (numbers[i] % 2 === 0) // Added else if so that we don't push the same number twice
        newNumbers.push(numbers[i])
}
console.log(newNumbers) 

// Values that are both divisible by 2 and 5 are pushed twice in the newNumbers array

<IPython.core.display.Javascript object>

Challenge

This code segment is at a very early stage of implementation.

  • What are some ways to (user) error proof this code?
  • The code should be able to calculate the cost of the meal of the user

Hint:

  • write a “single” test describing an expectation of the program of the program
  • test - input burger, expect output of burger price
  • run the test, which should fail because the program lacks that feature
  • write “just enough” code, the simplest possible, to make the test pass

Then repeat this process until you get program working like you want it to work.

%%js

var menu =  {"burger": 3.99,
         "fries": 1.99,
         "drink": 0.99}
var total = 0

// Shows the user the menu and prompts them to select items
console.log("Menu")
for (var item in menu) {
    console.log(item + "  $" + menu[item].toFixed(2)) // toFixed is used to format the price to 2 decimal places
}

// Ideally the code should support multiple items
var items = ["burger", "fries"] // Example items selected by the user

// Code should add the price of the menu items selected by the user 
for (var i = 0; i < items.length; i++) {
    var selectedItem = items[i];
    if (menu[selectedItem] !== undefined) {
        total += menu[selectedItem];
    } else {
        console.log("Item " + selectedItem + " is not on the menu.");
    }
}

console.log("Total: $" + total.toFixed(2));

<IPython.core.display.Javascript object>

Hacks

  • Fix the errors in the first three segments in this notebook and say what you changed in the code cell under “What I Changed” (Challenge is optional)